Imaging lens and imaging apparatus

ABSTRACT

The imaging lens includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. During focusing, only the second lens group moves in the direction of the optical axis. A lens closest to the object side in the first lens group and a lens adjacent to the lens on the image side have positive refractive powers, and the second lens group includes two or three lenses. Further, predetermined Conditional Expressions (1), (2), (3a), and (3b) are satisfied.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-197955 filed on Oct. 6, 2016. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an imaging lens, which is appropriate for electronic cameras such as a digital camera and a video camera, and an imaging apparatus which comprises the imaging lens.

Related Art

In the related art, as an imaging lens used in cameras in the above-mentioned field, an inner focus type imaging lens has been proposed in which focusing is performed by moving a part of the lens group in the middle portion of the lens system in the direction of the optical axis. Compared with an entire group extension type in which focusing is performed by moving the entire lens system, the inner focus type has an advantage that a light focusing operation and high-speed auto focusing control can be performed. For example, in JP5601598B, JP2012-242690A, and JP5628090B, in order from the object side, an inner focus type imaging lens, which includes first to third lens groups and performs focusing by moving the entirety or a part of the second lens group, has been proposed.

SUMMARY

In recent years, since the number of imaging pixels of a camera has increased, there has been a demand for the above-mentioned inner focus type imaging lens to correct various aberrations at a higher level. Further, there has been a demand for an imaging lens capable of performing focusing at a higher speed.

In the imaging lens described in JP5601598B, the number of lenses constituting the second lens group to be moved during focusing is large. Therefore, although fluctuations in various aberrations during focusing can be satisfactorily corrected, it is difficult to perform focusing at high speed. Further, in the imaging lenses described in JP2012-242690A and JP5628090B, since only one lens is moved during focusing, it is possible to perform focusing at high speed. However, in the case of one lens, it is difficult to suppress fluctuations in various aberrations during focusing. Furthermore, in the imaging lenses described in JP5601598B, JP2012-242690A, and JP5628090B, various aberrations are not sufficiently corrected.

The present invention has been made in view of the above situations, and an object of the present invention is to provide an inner focus type imaging lens, which is capable of performing focusing at high speed and suppressing fluctuations in various aberrations during focusing and in which various aberrations are satisfactorily corrected, and an imaging apparatus comprising the imaging lens.

According to the present invention, there is provided an imaging lens comprising, in order from an object side: a first lens group that has a positive refractive power; a second lens group that has a negative refractive power; and a third lens group that has a positive refractive power.

During focusing from an object at infinity to a closest object, only the second lens group moves in a direction of an optical axis.

A lens closest to the object side in the first lens group and a lens adjacent to the lens closest to the object side on an image side have positive refractive powers.

The second lens group includes two or three lenses.

The following conditional expression is satisfied.

0<AT/(CT11+CT12)<0.1  (1)

15<ν11<40  (2)

65<ν12<90  (3a)

0.0<θgF12−(−0.001682·ν12+0.6438)  (3b)

Here, CT11 is a center thickness of the lens closest to the object side in the first lens group on the optical axis,

CT12 is a center thickness of the lens adjacent to the lens closest to the object side on the image side in the first lens group on the optical axis,

AT is an air gap on the optical axis between the lens closest to the object side in the first lens group and the lens adjacent to the lens closest to the object side on the image side,

ν11 is an Abbe number of the lens closest to the object side in the first lens group,

ν12 is an Abbe number of the lens adjacent to the lens closest to the object side on the image side in the first lens group, and

θgF12 is a partial dispersion ratio of the lens adjacent to the lens closest to the object side on the image side in the first lens group between a g line and an F line.

In the imaging lens of the present invention, it is preferable that the first lens group has two groups of cemented lenses, where in each group, at least one lens having a positive refractive power and at least one lens having a negative refractive power are combined.

In the imaging lens of the present invention, it is preferable that the third lens group has two groups of cemented lenses, where in each group, at least one lens having a positive refractive power and at least one lens having a negative refractive power are combined.

In the imaging lens of the present invention, it is preferable that one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group includes a lens having a positive refractive power and a lens having a negative refractive power in order from the object side.

It is preferable that the following conditional expression is satisfied.

60<ν31<90  (4a)

0.0<θgF31−(−0.001682·ν31+0.6438)  (4b)

15<ν32<45  (5)

Here, ν31 is an Abbe number of the lens which has a positive refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group,

θgF31 is a partial dispersion ratio of the lens, which has a positive refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group, between the g line and the F line, and

ν32 is an Abbe number of the lens which has a negative refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group.

In the imaging lens of the present invention, it is preferable that one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group includes a lens having a positive refractive power and a lens having a negative refractive power in order from the object side.

It is preferable that the following conditional expression is satisfied.

60<ν33<80  (6a)

0.0<θgF33−(−0.001682·ν33+0.6438)  (6b)

15<ν34<35  (7)

Here, ν33 is an Abbe number of the lens which has a positive refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group,

θgF33 is a partial dispersion ratio of the lens, which has a positive refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group, between the g line and the F line, and

ν34 is an Abbe number of the lens which has a negative refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

−2.5<f/f2<−1.0  (8)

Here, f is a focal length of the whole system in a state where the object at infinity is in focus, and

f2 is a focal length of the second lens group.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

0.9<f/f1<1.5  (9)

Here, f is a focal length of the whole system in a state where the object at infinity is in focus, and

f1 is a focal length of the first lens group.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

1.0<f/f3<2.0  (10)

Here, f is a focal length of the whole system in a state where the object at infinity is in focus, and

f3 is a focal length of the third lens group.

In the imaging lens of the present invention, it is preferable that the second lens group includes two lenses, a lens close to the object side in the two lenses has a positive refractive power, a lens close to the image side in the two lenses has a negative refractive power, and the two lenses are cemented.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

1.70<N2<2.2  (11)

Here, N2 is a refractive index of the lens closest to the object side in the second lens group.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

15<ν21<30  (12)

Here, ν21 is an Abbe number of the lens closest to the object side in the second lens group.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

1.65<N1<2.2  (13)

Here, N1 is a refractive index of the lens closest to the object side in the first lens group.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

30<Δν1r<50  (14)

Here, Δν1r is a difference in Abbe number between a lens closest to the image side in the first lens group and a lens adjacent to the lens closest to the image side on the object side.

In the imaging lens of the present invention, it is preferable that an aperture stop is disposed between the first lens group and the second lens group, and the aperture stop remains stationary during focusing from the object at infinity to the closest object.

It is preferable that the imaging lens of the present invention satisfies the following conditional expression.

0.10<BF/f<0.50  (15)

Here, BF is an air conversion length from an image side surface of the lens, which is closest to the image side, to the image plane, and

f is a focal length of the whole system in a state where the object at infinity is in focus.

It is preferable that the imaging lens of the present invention satisfies any one of Conditional Expressions (1-1), (1-2), (3a-1), and (3b-1). In addition, the imaging lens of the present invention may satisfy any one of Conditional Expressions (1) to (15), (1-1), (1-2), (3a-1) and (3b-1), or may satisfy an arbitrary combination thereof.

0.005<AT/(CT11+CT12)<0.05  (1-1)

20<ν11<36  (2-1)

65<ν12<85  (3a-1)

0.01<θgF12−(−0.001682·ν12+0.6438)<0.1  (3b-1)

Here, CT11 is a center thickness of the lens closest to the object side in the first lens group on the optical axis,

CT12 is a center thickness of the lens adjacent to the lens closest to the object side on the image side in the first lens group on the optical axis,

AT is an air gap on the optical axis between the lens closest to the object side in the first lens group and the lens adjacent to the lens closest to the object side on the image side,

ν11 is an Abbe number of the lens closest to the object side in the first lens group,

ν12 is an Abbe number of the lens adjacent to the lens closest to the object side on the image side in the first lens group, and

θgF12 is a partial dispersion ratio of the lens adjacent to the lens closest to the object side on the image side in the first lens group between a g line and an F line.

An imaging apparatus of the present invention comprises the imaging lens of the present invention.

The term “comprises ˜” means that the lens may include not only the lens groups or the lenses as elements but also lenses substantially having no powers, optical elements, which are not lenses, such as a stop, a mask, a cover glass, and a filter, and mechanism parts such as a lens flange, a lens barrel, an imaging element, and a hand shaking correction mechanism.

Further, the “lens group” is not necessarily formed of a plurality of lenses, but may be formed as only one lens. The term “˜ lens group that has a positive refractive power” means that the lens group has a positive refractive power as a whole. It is the same for the term “˜ lens group that has a negative refractive power”.

Reference signs of refractive powers of the lenses, surface shapes of the lenses, and radii of curvature of surfaces of the lenses are assumed as those in paraxial regions in a case where some lenses have aspheric surfaces. Reference signs of radii of curvature of surface shapes convex toward the object side are set to be positive, and reference signs of radii of curvature of surface shapes convex toward the image side are set to be negative. Further, in the present invention, the conditional expressions relate to the d line (a wavelength of 587.6 nm) unless otherwise specified.

According to the present invention, the imaging lens includes, in order from an object side: the first lens group that has a positive refractive power; the second lens group that has a negative refractive power; and the third lens group that has a positive refractive power. During focusing from the object at infinity to the closest object, only the second lens group moves in the direction of the optical axis. The lens closest to the object side in the first lens group and the lens adjacent to the lens closest to the object side on the image side have positive refractive powers. The second lens group includes two or three lenses. Conditional Expressions (1), (2), (3a), and (3b) are satisfied. Hence, it is possible to perform focusing at high speed while suppressing fluctuations in various aberrations during focusing, and it is possible to satisfactorily correct various aberrations.

Further, the imaging apparatus of the present invention comprises the imaging lens of the present invention. Thus, it is possible to perform focusing at high speed, and it is possible to obtain high quality videos.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a lens configuration of an imaging lens (common to Example 1) according to an embodiment of the present invention.

FIG. 2 is an optical path diagram of an imaging lens (common to Example 1) according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 2 of the present invention.

FIG. 4 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 3 of the present invention.

FIG. 5 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 4 of the present invention.

FIG. 6 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 5 of the present invention.

FIG. 7 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 6 of the present invention.

FIG. 8 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 7 of the present invention.

FIG. 9 is a cross-sectional view illustrating a lens configuration of an imaging lens of Example 8 of the present invention.

FIG. 10 is a diagram of aberrations of the imaging lens of Example 1 of the present invention.

FIG. 11 is a diagram of aberrations of the imaging lens of Example 2 of the present invention.

FIG. 12 is a diagram of aberrations of the imaging lens of Example 3 of the present invention.

FIG. 13 is a diagram of aberrations of the imaging lens of Example 4 of the present invention.

FIG. 14 is a diagram of aberrations of the imaging lens of Example 5 of the present invention.

FIG. 15 is a diagram of aberrations of the imaging lens of Example 6 of the present invention.

FIG. 16 is a diagram of aberrations of the imaging lens of Example 7 of the present invention.

FIG. 17 is a diagram of aberrations of the imaging lens of Example 8 of the present invention.

FIG. 18 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention as viewed from the front side.

FIG. 19 is a schematic configuration diagram of an imaging apparatus according to the embodiment of the present invention as viewed from the rear side.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described with reference to drawings. FIG. 1 is a cross-sectional view illustrating a lens configuration of an imaging lens (common to Example 1) according to an embodiment of the present invention. The exemplary configuration shown in FIG. 1 is the same as the configuration of the imaging lens of Example 1 to be described later. In FIG. 1, the left side is the object side, and the right side is the image side. Further, FIG. 2 shows an optical path diagram of an imaging lens according to an embodiment shown in FIG. 1, and shows optical paths of on-axis rays 2 and rays with the maximum angle of view 3 from the object point at the infinite distance. FIGS. 1 and 2 and FIGS. 3 to 9 to be described later show lens configurations in a state where the object at infinity is in focus.

As shown in FIGS. 1 and 2, the imaging lens of the present embodiment includes, in order from the object side along an optical axis Z, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power. An aperture stop St is disposed between the first lens group G1 and the second lens group G2. It should be noted that the aperture stop St does not necessarily indicate its size and shape, and indicates a position of the stop on the optical axis Z. Further, an inner focus type, in which only the second lens group G2 moves toward the image side in the direction of the optical axis during focusing from the object at infinity to the closest object, is employed. In addition, during focusing, the first lens group G1, the third lens group G3, and the aperture stop St do not move.

In the example shown in FIG. 1, the first lens group G1 includes, in order from the object side, six lenses, that is, lenses L11 to L16, the second lens group G2 includes, in order from the object side, two lenses, that is, lenses L21 and L22, and the third lens group G3 includes, in order from the object side, six lenses, that is, lenses L31 to L36. However, each lens group may include lenses of which the number is different from that in the example shown in FIG. 1. In particular, the second lens group G2 may include three lenses.

In a case where the imaging lens of the present embodiment is intended to be applied to an imaging apparatus, in accordance with a configuration of a camera on which the lens is mounted, it is preferable that a cover glass, a prism, and various filters such as an infrared cut filter and a lowpass filter are disposed between the optical system and the image plane Sim. Thus, FIG. 1 shows an example in which an optical member PP of a plane-parallel plate assumed as the above-mentioned elements is disposed between the lens system and the image plane Sim.

In the imaging lens of the present embodiment, the lens L11 closest to the object side in the first lens group G1 and the lens L12 adjacent to the lens L11 closest to the object side on the image side have positive refractive powers.

The imaging lens of the present embodiment is configured to satisfy Conditional Expressions (1), (2), (3a), and (3b).

0<AT/(CT11+CT12)<0.1  (1)

15<ν11<40  (2)

65<ν12<90  (3a)

0.0<θgF12−(−0.001682·ν12+0.6438)  (3b)

Here, CT11 is a center thickness of the lens L11 closest to the object side in the first lens group G1 on the optical axis,

CT12 is a center thickness of the lens L12 adjacent to the lens L11 closest to the object side on the image side in the first lens group G1 on the optical axis,

AT is an air gap on the optical axis between the lens L11 closest to the object side in the first lens group G1 and the lens L12 adjacent to the lens L11 closest to the object side on the image side,

ν11 is an Abbe number of the lens L11 closest to the object side in the first lens group G1,

ν12 is an Abbe number of the lens L12 adjacent to the lens L11 closest to the object side on the image side in the first lens group G1, and

θgF12 is a partial dispersion ratio of the lens L12 adjacent to the lens L11 closest to the object side on the image side in the first lens group G1 between a g line and an F line.

The imaging lens of the present embodiment is configured such that only the second lens group G2 moves toward the image side in the direction of the optical axis during focusing from the object at infinity to the closest object. Therefore, it is possible to reduce the weight of the focusing group. As a result, it is possible to perform focusing at high speed. Further, it is possible to reduce the size of the lens system.

Further, by making the second lens group G2 include two or three lenses, fluctuations in various aberrations can be suppressed during focusing from the infinity to the close-range object.

Further, by making the lens L11 closest to the object side in the first lens group G1 and the lens L12 adjacent to the lens L11 closest to the object side on the image side have positive refractive powers and by not allowing the result of Conditional Expressions (1) to be equal to or less than the lower limit, the two lenses L11 and L12 are prevented from interfering with each other at the time of manufacturing. Thereby, it is possible to prevent trouble from occurring at the time of manufacturing. Furthermore, by making the lens L11 closest to the object side in the first lens group G1 and the lens L12 adjacent to the lens L11 closest to the object side on the image side have positive refractive powers and by not allowing the result of Conditional Expressions (1) to be equal to or greater than the upper limit, it is possible to shorten the total length of the lens system. In addition, it is possible to minimize the height of the on-axis rays, which are incident into the second lens group G2, and minimize the size of the entire diameter of the second lens group G2.

By simultaneously satisfying Conditional Expressions (2) and (3a) in combination of the Abbe numbers and satisfying Conditional Expression (3b) in the partial dispersion ratio, it is possible to satisfactorily correct chromatic aberration. In particular, by not allowing the result of Conditional Expression (2) to be equal to or less than the lower limit and not allowing the result of Conditional Expressions (3a) and (3b) to be equal to or greater than the upper limit, it is possible to prevent chromatic aberration from being excessively corrected.

In order to more enhance at least one of the effects of Conditional Expressions (1), (2), (3a), and (3b), it is preferable that at least one of Conditional Expression (1-1), (2-1), (3a-1) or (3b-1) is satisfied.

0.005<AT/(CT11+CT12)<0.05  (1-1)

20<ν11<36  (2-1)

65<ν12<85  (3a-1)

0.01<θgF12−(−0.001682·ν12+0.6438)<0.1  (3b-1)

Further, in the imaging lens of the present embodiment, it is preferable that the first lens group G1 has two groups of cemented lenses, where in each group, at least one lens having a positive refractive power and at least one lens having a negative refractive power are combined. Thereby, there is an advantage in correction of chromatic aberration. In addition, in the imaging lens of the present embodiment shown in FIG. 1, the first lens group G1 has two groups of cemented lenses including: cemented lenses in which a lens L13 having a negative refractive power and a lens L14 having a positive refractive power are combined; and cemented lenses in which a lens L15 having a negative refractive power and a lens L16 having a positive refractive power are combined.

Further, in the imaging lens of the present embodiment, it is preferable that the third lens group G3 has two groups of cemented lenses, where in each group, at least one lens having a positive refractive power and at least one lens having a negative refractive power are combined. Thereby, there is an advantage in correction of chromatic aberration. In addition, in the imaging lens of the present embodiment shown in FIG. 1, the third lens group G3 has two groups of cemented lenses including: cemented lenses in which a lens L31 having a positive refractive power and a lens L32 having a negative refractive power are combined; and cemented lenses in which a lens L33 having a positive refractive power and a lens L34 having a negative refractive power are combined.

Further, in the imaging lens of the present embodiment, it is preferable that one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group G3 includes a lens L31 having a positive refractive power and a lens L32 having a negative refractive power in order from the object side, and Conditional Expressions (4a), (4b), and (5) are satisfied.

60<ν31<90  (4a)

0.0<θgF31−(−0.001682·ν31+0.6438)  (4b)

15<ν32<45  (5)

Here, ν31 is an Abbe number of the lens L31 which has a positive refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group G3,

θgF31 is a partial dispersion ratio of the lens L31, which has a positive refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group G3, between the g line and the F line, and

ν32 is an Abbe number of the lens L32 which has a negative refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group G3.

By simultaneously satisfying Conditional Expressions (4a) and (5) in combination of the Abbe numbers and satisfying Conditional Expression (4b) in the partial dispersion ratio, it is possible to satisfactorily correct chromatic aberration. In particular, by not allowing the result of Conditional Expression (5) to be equal to or less than the lower limit and not allowing the result of Conditional Expressions (4a) and (4b) to be equal to or greater than the upper limit, it is possible to prevent chromatic aberration from being excessively corrected.

In order to more enhance at least one of the effects of Conditional Expressions (4a), (4b), and (5), it is preferable that at least one of Conditional Expression (4a-1), (4b-1), or (5-1) is satisfied.

65<ν31<85  (4a-1)

0.01<θgF31−(−0.001682·ν31+0.6438)<0.2  (4b-1)

20<ν32<38  (5-1)

Further, in the imaging lens of the present embodiment, it is preferable that one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group G3 includes a lens L33 having a positive refractive power and a lens L34 having a negative refractive power in order from the object side, and Conditional Expressions (6a), (6b), and (7) are satisfied.

60<ν33<80  (6a)

0.0<θgF33−(−0.001682·ν33+0.6438)  (6b)

15<ν34<35  (7)

Here, ν33 is an Abbe number of the lens L33 which has a positive refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group G3,

θgF33 is a partial dispersion ratio of the lens L33, which has a positive refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group G3, between the g line and the F line, and

ν34 is an Abbe number of the lens L34 which has a negative refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group G3.

By simultaneously satisfying Conditional Expressions (6a) and (7) in combination of the Abbe numbers and satisfying Conditional Expression (6b) in the partial dispersion ratio, it is possible to satisfactorily correct chromatic aberration. In particular, by not allowing the result of Conditional Expression (7) to be equal to or less than the lower limit and not allowing the result of Conditional Expressions (6a) and (6b) to be equal to or greater than the upper limit, it is possible to prevent chromatic aberration from being excessively corrected.

In order to more enhance at least one of the effects of Conditional Expressions (6a), (6b), and (7), it is preferable that at least one of Conditional Expression (6a-1), (6b-1), or (7-1) is satisfied.

65<ν33<75  (6a-1)

0.01<θgF33−(−0.001682·ν33+0.6438)<0.1  (6b-1)

20<ν34<30  (7-1)

It is preferable that Conditional Expression (8) is satisfied.

−2.5<f/f2<−1.0  (8)

Here, f is a focal length of the whole system in a state where the object at infinity is in focus, and

f2 is a focal length of the second lens group G2.

By not allowing the result of Conditional Expression (8) to be equal to or less than the lower limit, the refractive power of the second lens group G2 is prevented from becoming excessively strong, it is possible to suppress fluctuations in spherical aberration, astigmatism, and chromatic aberration caused by focusing Thereby, it is possible to obtain favorable optical performance on the proximity side. By not allowing the result of Conditional Expression (8) to be equal to or greater than the upper limit, it is possible to minimize the amount of movement of the second lens group G2 during focusing. Thus, it is possible to shorten a period of time up to focusing. Thereby, it is possible to perform focusing at high speed. Further, it becomes easy to secure a space for arranging mechanical components on the object side and the image side of the second lens group G2.

In order to more enhance the effect of Conditional Expression (8), it is more preferable that Conditional Expression (8-1) is satisfied.

−2.2<f/f2<−1.4  (8-1)

It is preferable that Conditional Expression (9) is satisfied.

0.9<f/f1<1.5  (9)

Here, f is a focal length of the whole system in a state where the object at infinity is in focus, and

f1 is a focal length of the first lens group G1.

By not allowing the result of Conditional Expression (9) to be equal to or less than the lower limit, it is possible to secure the positive refractive power of the first lens group G1. Thus, it is possible to shorten the total length of the lens system. By not allowing the result of Conditional Expression (9) to be equal to or greater than the upper limit, it is possible to suppress the positive refractive power of the first lens group G1. Thus, it is possible to suppress spherical aberration and astigmatism.

In order to more enhance the effect of Conditional Expression (9), it is more preferable that Conditional Expression (9-1) is satisfied.

1.0<f/f1<1.4  (9-1)

It is preferable that Conditional Expression (10) is satisfied.

1.0<f/f3<2.0  (10)

Here, f is a focal length of the whole system in a state where the object at infinity is in focus, and

f3 is a focal length of the third lens group G3.

By not allowing the result of Conditional Expression (10) to be equal to or less than the lower limit, it is possible to secure the positive refractive power of the third lens group G3. Thus, it is possible to shorten the total length of the lens system. By not allowing the result of Conditional Expression (10) to be equal to or greater than the upper limit, it is possible to suppress the positive refractive power of the third lens group G3. Thus, it is possible to suppress spherical aberration and astigmatism.

In order to more enhance the effect of Conditional Expression (10), it is more preferable that Conditional Expression (10-1) is satisfied.

1.2<f/f3<1.8  (10-1)

Further, it is preferable that the second lens group G2 includes two lenses L21 and L22, the lens L21 close to the object side in the two lenses has a positive refractive power, the lens L22 close to the image side in the two lenses has a negative refractive power, and the two lenses L21 and L22 are cemented. Thereby, longitudinal chromatic aberration and it is possible to satisfactorily correct lateral chromatic aberration.

It is preferable that Conditional Expression (11) is satisfied.

1.70<N2<2.2  (11)

Here, N2 is a refractive index of the lens closest to the object side in the second lens group G2.

By not allowing the result of Conditional Expression (11) to be equal to or less than the lower limit, it is possible to suppress fluctuations in various aberrations during focusing. By not allowing the result of Conditional Expression (11) to be equal to or greater than the upper limit, it is possible to suppress an increase in amount of movement of the second lens group G2 during focusing from the infinity to the close-range object. Thereby, it is possible to suppress an increase in total length of the lens system.

In order to more enhance the effect of Conditional Expression (11), it is more preferable that Conditional Expression (11-1) is satisfied.

1.80<N2<2.2  (11-1)

It is preferable that Conditional Expression (12) is satisfied.

15<ν21<30  (12)

Here, ν21 is an Abbe number of the lens L21 closest to the object side in the second lens group G2.

By not allowing the result of Conditional Expression (12) to be equal to or less than the lower limit, it is possible to satisfactorily correct chromatic aberration. By not allowing the result of Conditional Expression (12) to be equal to or greater than the upper limit, it is possible to prevent chromatic aberration from being excessively corrected.

In order to more enhance the effect of Conditional Expression (12), it is more preferable that Conditional Expression (12-1) is satisfied.

15<ν21<25  (12-1)

It is preferable that Conditional Expression (13) is satisfied.

1.65<N1<2.2  (13)

Here, N1 is a refractive index of the lens L11 closest to the object side in the first lens group G1.

By not allowing the result of Conditional Expression (13) to be equal to or less than the lower limit, it is possible to suppress an increase in total length of the lens system. By not allowing the result of Conditional Expression (13) to be equal to or greater than the upper limit, it is possible to satisfactorily correct spherical aberration.

In order to more enhance the effect of Conditional Expression (13), it is more preferable that Conditional Expression (13-1) is satisfied.

1.70<N1<2.1  (13-1)

It is preferable that Conditional Expression (14) is satisfied.

30<Δν1r<50  (14)

Here, Δν1r is a difference in Abbe number between a lens L16 closest to the image side in the first lens group G1 and a lens L15 adjacent to the lens L16 closest to the image side on the object side.

By not allowing the result of Conditional Expression (14) to be equal to or less than the lower limit, it is possible to satisfactorily correct chromatic aberration. By not allowing the result of Conditional Expression (14) to be equal to or greater than the upper limit, it is possible to prevent chromatic aberration from being excessively corrected.

In order to more enhance the effect of Conditional Expression (14), it is more preferable that Conditional Expression (14-1) is satisfied.

35<Δν1r<46  (14-1)

It is preferable that an aperture stop St is disposed between the first lens group G1 and the second lens group G2, and the aperture stop St remains stationary during focusing from the object at infinity to the closest object. By disposing the aperture stop St between the first lens group G1 and the second lens group G2, it is possible to suppress fluctuation in angle of view, that is, fluctuation in image magnification occurring in the vicinity of the focal plane during focusing. Further, by making the aperture stop St remain stationary during focusing, it is possible to reduce the weight of the focusing part. Thus, it is possible to perform focusing at high speed.

It is preferable that Conditional Expression (15) is satisfied.

0.10<BF/f<0.50  (15)

Here, BF is an air conversion length from an image side surface of the lens, which is closest to the image side, to the image plane, and

f is a focal length of the whole system in a state where the object at infinity is in focus.

By not allowing the result of Conditional Expression (15) to be equal to or less than the lower limit, it is possible to secure a back focal length necessary for an interchangeable lens. By not allowing the result of Conditional Expression (15) to be equal to or greater than the upper limit, it is possible to suppress the total length of the lens system.

In order to more enhance the effect of Conditional Expression (15), it is more preferable that Conditional Expression (15-1) is satisfied.

0.15<BF/f<0.45  (15-1)

In the imaging lens of the present embodiment, as the material closest to the object side, specifically, glass is preferably used, or transparent ceramics may be used.

In a case where the imaging lens of the present embodiment is used under a severe environment, it is preferable to apply a multilayer film coating for protection. Not only the protective coating but also antireflective coating for reducing ghost light in use may be performed.

In the example shown in FIG. 1, the optical member PP is disposed between the lens system and the image plane Sim. However, various filters such as a lowpass filter or a filter for cutting off a specific wavelength region may not be disposed between the lens system and the image plane Sim. Instead, such various filters may be disposed between the lenses, or coating for functions the same as those of various filters may be performed on a lens surface of any lens.

The above-mentioned preferred configurations and available configurations including the configurations relating to Conditional Expressions may be arbitrary combinations, and it is preferable to selectively adopt the configurations in accordance with required specification. For example, the imaging lens according to the present embodiment satisfies Conditional Expressions (1), (2), (3a), and (3b), but may satisfy any one of Conditional Expressions (1) to (15) and Conditional Expressions (1-1) to (15-1), and may satisfy an arbitrary combination of Conditional Expressions.

Next, numerical examples of the imaging lens of the present invention will be described.

First, the imaging lens of Example 1 will be described. FIG. 1 is a cross-sectional view illustrating a lens configuration of the imaging lens of Example 1. In addition, in FIG. 1 and FIGS. 2 to 8 corresponding to Examples 3 to 9, the optical member PP is additionally shown. Further, the left side is an object side, and the right side is an image side. In addition, an aperture stop St shown in the drawing does not necessarily show its real size and shape, but show a position on an optical axis Z.

Table 1 shows basic lens data of the imaging lens 1 of Example, Table 2 shows data about specification, and Table 3 shows data about moved surface spacings. Hereinafter, meanings of the reference signs in the tables are, for example, as described in Example 1, and are basically the same as those in Examples 2 to 8.

In the lens data of Table 1, the column of Si shows i-th (i=1, 2, 3, . . . ) surface number. The i-th surface number sequentially increases toward the image side in a case where a surface of an element closest to the object side is regarded as a first surface. The column of Ri shows a radius of curvature of the i-th surface. The column of Di shows a surface spacing on the optical axis Z between the i-th surface and an (i+1)th surface. Further, the column of Ndj shows a refractive index of a j-th (j=1, 2, 3, . . . ) optical element at the d line (a wavelength of 587.6 nm), where j sequentially increases toward the image side in a case where the optical element closest to the object side is regarded as the first element. The column of vdj shows an Abbe number of the j-th optical element on the basis of the d line (a wavelength of 587.6 nm).

It should be noted that the sign of the radius of curvature is positive in a case where a surface has a shape convex toward the object side, and is negative in a case where a surface has a shape convex toward the image side. The basic lens data additionally shows the aperture stop St and the optical member PP. In a place of a surface number of a surface corresponding to the aperture stop St, the surface number and a term of (stop) are noted. Further, in the lens data of Table 1, in each place of the surface spacing which is variable during focusing, DD[i] is noted.

In the data about the specification of Table 2, values of the focal length f, the back focal length BF, the F number FNo., and the total angle of view 2ω of the whole system in a state where the object at infinity is in focus are noted. Further, in the data about the moved surface spacings of Table 3, moved surface spacings respectively in a state where the object at infinity is in focus and in a state where the closest object is in focus (at a distance of 110 cm) are denoted.

In data of each table, a degree is used as a unit of an angle, and mm is used as a unit of a length, but appropriate different units may be used since the optical system can be used even in a case where the system is enlarged or reduced in proportion. Further, each of the following tables shows numerical values rounded off to predetermined decimal places.

TABLE 1 Example 1•Lens Data Si Ri Di Ndj ν dj  1 98.0201 3.9500 1.95375 32.32  2 265.8358 0.1000  3 106.1474 5.3200 1.55032 75.50  4 −625.6445 0.3600  5 ∞ 1.7300 1.56732 42.81  6 49.3830 5.9800 1.88300 39.22  7 192.1886 1.4900  8 ∞ 1.7000 1.63980 34.49  9 30.7780 10.1000 1.55032 75.50 10 ∞ 6.0100 11(stop) ∞ DD[11] 12 −380.4254 3.0700 1.95906 17.47 13 −70.6290 1.2200 1.85150 40.78 14 51.2612 DD[14] 15 −230.3817 5.1800 1.55032 75.50 16 −39.2300 1.6300 1.68893 31.16 17 −102.2608 0.1000 18 48.4494 8.7500 1.59282 68.62 19 −82.6540 1.8000 1.76182 26.61 20 82.6540 9.9600 21 119.8382 7.0400 2.00100 29.13 22 −96.6341 19.5100 23 −37.7586 1.4700 1.51680 64.21 24 −163.9992 23.8566 25 ∞ 3.2000 1.51680 64.20 26 ∞ 1.0003

TABLE 2 Example 1•Specification f 108.47 BF 26.97 FNo. 2.06 2ω[°] 29.8

TABLE 3 Example 1•Moved surface Spacing Infinity 110 cm DD[11] 4.7000 13.31 DD[14] 18.1900 9.58

FIG. 10 shows a diagram of aberrations of the imaging lens of Example 1. In addition, in order from the upper left side of FIG. 10, spherical aberration, astigmatism, distortion, and lateral chromatic aberration in a state where the focus is at infinity are shown. In order from the lower left side of FIG. 10, spherical aberration, astigmatism, distortion, and lateral chromatic aberration in a state where the focus is in a closest range (at a distance of 110 cm) are shown. The diagram of aberrations illustrating spherical aberration, astigmatism, and distortion indicates aberrations that occur in a case where the d line (a wavelength of 587.6 nm) is set as a reference wavelength. In the spherical aberration diagram, aberrations at the d line (a wavelength of 587.6 nm), the C line (a wavelength of 656.3 nm), the F line (a wavelength of 486.1 nm), and the g line (a wavelength of 435.8 nm) are respectively indicated by the solid line, the long dashed line, the short dashed line, and the gray solid line. In the astigmatism diagram, aberrations in sagittal and tangential directions are respectively indicated by the solid line and the short dashed line. In the lateral chromatic aberration diagram, aberrations at the C line (a wavelength of 656.3 nm), the F line (a wavelength of 486.1 nm), and the g line (a wavelength of 435.8 nm) are respectively indicated by the long dashed line, the short dashed line, and the gray solid line. In the spherical aberration diagram, FNo. indicates an F number. In the other aberration diagrams, w indicates a half angle of view.

In the description of Example 1, reference signs, meanings, and description methods of the respective data pieces are the same as those in the following examples unless otherwise noted. Therefore, in the following description, repeated description will be omitted.

Next, an imaging lens of Example 2 will be described. FIG. 3 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 2. The imaging lens of Example 2 has the same lens groups and has the same number of lenses as that of Example 1. Table 4 shows lens data of the imaging lens of Example 2, Table 5 shows data about specification, and Table 6 shows data about moved surface spacings. FIG. 11 shows a diagram of aberrations thereof

TABLE 4 Example 2•Lens Data Si Ri Di Ndj ν dj  1 106.3848 3.5384 1.95375 32.32  2 265.6927 0.1000  3 101.7009 5.4244 1.55032 75.50  4 −630.1370 0.3749  5 ∞ 1.7116 1.56732 42.82  6 52.8020 5.6122 1.88300 39.22  7 199.7038 1.4361  8 ∞ 1.7023 1.60342 38.03  9 28.8426 10.8019 1.55032 75.50 10 ∞ 5.9340 11(stop) ∞ DD[11] 12 −327.2908 3.5884 1.84666 23.88 13 −56.2879 1.2056 1.78800 47.37 14 49.3882 DD[14] 15 −438.1328 5.2541 1.55032 75.50 16 −37.9595 1.5318 1.61293 37.01 17 −154.6615 0.1000 18 48.3799 10.1945 1.59282 68.62 19 −77.7556 1.8396 1.78470 26.29 20 77.7556 9.6988 21 114.3439 6.4986 2.00100 29.13 22 −92.0720 19.3196 23 −38.6067 1.5176 1.51680 64.20 24 −155.0998 23.7721 25 ∞ 3.2000 1.51680 64.20 26 ∞ 1.0212

TABLE 5 Example 2•Specification f 107.27 BF 26.90 FNo. 2.06 2ω[°] 30.2

TABLE 6 Example 2•Moved surface Spacing Infinity 110 cm DD[11] 4.5904 13.06 DD[14] 17.8292 9.35

Next, an imaging lens of Example 3 will be described. FIG. 4 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 3. The imaging lens of Example 3 has the same lens groups and has the same number of lenses as that of Example 1. Table 7 shows lens data of the imaging lens of Example 3, Table 8 shows data about specification, and Table 9 shows data about moved surface spacings. FIG. 12 shows a diagram of aberrations thereof

TABLE 7 Example 3•Lens Data Si Ri Di Ndj ν dj  1 110.1353 3.4495 1.95375 32.32  2 265.6927 0.1000  3 99.4077 5.5109 1.55032 75.50  4 −630.1370 0.3633  5 ∞ 1.7116 1.56732 42.82  6 52.9064 5.6714 1.88300 39.22  7 211.7495 1.3537  8 ∞ 1.7018 1.60342 38.03  9 28.9785 10.7364 1.55032 75.50 10 ∞ 5.9336 11(stop) ∞ DD[11] 12 −307.9404 3.5884 1.85896 22.73 13 −57.5212 1.2056 1.78800 47.37 14 49.4170 DD[14] 15 −438.0952 5.7397 1.55032 75.50 16 −34.7529 1.5321 1.61293 37.01 17 −161.1969 0.1000 18 48.7483 10.4064 1.59282 68.62 19 −76.6654 1.8400 1.76182 26.52 20 76.6654 9.4094 21 115.1430 6.9920 2.00100 29.13 22 −92.0934 19.3196 23 −38.2519 1.5635 1.51680 64.20 24 −140.3347 23.8233 25 ∞ 3.2000 1.51680 64.20 26 ∞ 1.0178

TABLE 8 Example 3•Specification f 106.94 BF 26.95 FNo. 2.06 2ω[°] 30.2

TABLE 9 Example 3•Moved surface Spacing Infinity 110 cm DD[11] 4.6727 13.12 DD[14] 17.7604 9.31

Next, an imaging lens of Example 4 will be described. FIG. 5 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 4. The imaging lens of Example 4 has a configuration having the same number of lens groups and the same number of lenses as those of Example 1 except that the lens L12, the lens L13, and the lens L14 are cemented lenses in the first lens group G1. Table 10 shows lens data of the imaging lens of Example 4, Table 11 shows data about specification, and Table 12 shows data about moved surface spacings. FIG. 13 shows a diagram of aberrations thereof.

TABLE 10 Example 4•Lens Data Si Ri Di Ndj νdj  1 107.3080 4.1739 1.95375 32.32  2 456.5514 0.0916  3 91.2967 6.8951 1.53775 74.70  4 −213.6548 1.7216 1.56732 42.82  5 47.0462 5.3074 1.88300 40.76  6 109.2640 1.7362  7 211.7188 1.7016 1.63980 34.47  8 31.7422 9.0693 1.53775 74.70  9 537.2566 7.3712 10 (stop) ∞ DD[10] 11 −461.3564 2.8696 1.95906 17.47 12 −82.1465 1.2980 1.85150 40.78 13 54.5189 DD[13] 14 −356.0335 4.4264 1.53775 74.70 15 −43.5657 1.5410 1.68893 31.07 16 −121.0697 0.0457 17 47.6863 12.8904 1.59522 67.73 18 −76.6387 1.9783 1.72825 28.46 19 69.6963 6.6427 20 101.0643 6.8080 2.00100 29.13 21 −103.6279 18.9064 22 −37.0799 1.6096 1.51680 64.20 23 −152.7629 22.3000 24 ∞ 3.2000 1.51680 64.20 25 ∞ 1.0160

TABLE 11 Example 4•Specification f 108.71 BF 25.43 FNo. 2.06 2ω [°] 29.8

TABLE 12 Example 4•Moved surface Spacing Infinity 110 cm DD[10] 4.8321 14.94 DD[13] 20.4938 10.38

Next, an imaging lens of Example 5 will be described. FIG. 6 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 5. The imaging lens of Example 5 has a configuration having the same number of lens groups and the same number of lenses as those of Example 1 except that the third lens group G3 includes seven lenses including the lenses L31 to L37 in order from the object side. Table 13 shows lens data of the imaging lens of Example 5, Table 14 shows data about specification, and Table 15 shows data about moved surface spacings. FIG. 14 shows a diagram of aberrations thereof

TABLE 13 Example 5•Lens Data Si Ri Di Ndj νdj  1 118.8923 3.4500 1.95375 32.32  2 265.6927 0.1000  3 90.8382 5.9804 1.59282 68.62  4 −543.6406 0.2822  5 ∞ 1.8501 1.51742 52.43  6 53.3507 5.9800 1.88300 39.22  7 204.6480 1.4219  8 ∞ 1.7715 1.63980 34.49  9 31.6829 10.4552 1.55032 75.50 10 ∞ 5.9804 11 (stop) ∞ DD[11] 12 −297.7140 3.2827 2.10420 17.02 13 −81.2978 1.2291 1.88300 39.22 14 50.0806 DD[14] 15 −184.4306 3.2308 1.55032 75.50 16 −55.0988 1.5319 1.68893 31.16 17 −102.2200 0.1000 18 51.2965 8.7496 1.59282 68.62 19 −65.7152 1.8397 1.76182 26.61 20 83.9313 12.9513 21 115.5111 7.0859 1.95375 32.32 22 −93.5426 21.1712 23 −41.0671 1.5636 1.48749 70.24 24 −1241.5142 0.9200 25 1931.9069 2.9896 1.88300 39.22 26 −413.8329 19.8351 27 ∞ 3.2000 1.51680 64.20 28 ∞ 1.0148

TABLE 14 Example 5•Specification f 109.94 BF 22.96 FNo. 2.07 2ω [°] 29.2

TABLE 15 Example 5•Moved surface Spacing Infinity 110 cm DD[11] 4.4967 12.28072 DD[14] 17.4796 9.69559

Next, an imaging lens of Example 6 will be described. FIG. 7 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 6. The imaging lens of Example 6 has the same lens groups and has the same number of lenses as that of Example 1. Table 16 shows lens data of the imaging lens of Example 6, Table 17 shows data about specification, and Table 18 shows data about moved surface spacings. FIG. 15 shows a diagram of aberrations thereof

TABLE 16 Example 6•Lens Data Si Ri Di Ndj νdj  1 87.9707 4.6072 1.91082 35.25  2 265.6927 0.1000  3 86.9451 5.9801 1.49700 81.61  4 −874.2744 0.5169  5 ∞ 1.8503 1.51742 52.43  6 65.0251 4.5996 1.88300 39.22  7 158.2965 1.7996  8 ∞ 1.7714 1.63980 34.49  9 31.9636 10.3262 1.55032 75.50 10 ∞ 5.4736 11 (stop) ∞ DD[11] 12 2965.9301 3.5984 1.86631 21.68 13 −65.0753 1.5185 1.88300 39.22 14 52.6520 DD[14] 15 −270.6026 3.8493 1.55032 75.50 16 −56.5189 1.6333 1.68893 31.16 17 −114.5219 0.1000 18 47.3377 10.4058 1.59282 68.62 19 −83.0299 1.8404 1.76182 26.61 20 83.0299 9.5033 21 111.7491 6.8612 2.00100 29.13 22 −104.9887 18.8425 23 −37.9292 1.5636 1.51680 64.20 24 −576.1539 20.7531 25 ∞ 3.2000 1.51680 64.20 26 ∞ 1.0274

TABLE 17 Example 6•Specification f 108.53 BF 23.89 FNo. 2.06 2ω [°] 29.8

TABLE 18 Example 6•Moved surface Spacing Infinity 110 cm DD[11] 4.3959 13.90004 DD[14] 19.5212 10.01704

Next, an imaging lens of Example 7 will be described. FIG. 8 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 7. The imaging lens of Example 7 has the same lens groups and has the same number of lenses as that of Example 1. Table 19 shows lens data of the imaging lens of Example 7, Table 20 shows data about specification, and Table 21 shows data about moved surface spacings. FIG. 16 shows a diagram of aberrations thereof

TABLE 19 Example 7•Lens Data Si Ri Di Ndj νdj  1 98.6329 4.0685 1.95375 32.32  2 265.6927 0.1000  3 84.9775 5.9801 1.49700 81.61  4 −867.6957 0.5145  5 ∞ 1.8500 1.51742 52.43  6 68.1251 4.5996 1.88300 39.22  7 182.1538 1.5902  8 ∞ 1.7714 1.63980 34.49  9 34.1208 9.6667 1.55032 75.50 10 ∞ 8.1424 11 (stop) ∞ DD[11] 12 2866.8705 3.5980 1.84913 22.54 13 −65.5911 1.5184 1.88300 39.22 14 53.9698 DD[14] 15 −270.5866 3.9948 1.59319 67.90 16 −53.9096 1.6333 1.68893 31.16 17 −102.2223 0.1000 18 49.5222 10.4064 1.59319 67.90 19 −79.5798 1.8404 1.76182 26.61 20 79.5798 10.9962 21 115.6491 6.9901 2.00100 29.13 22 −96.9807 16.9467 23 −42.5912 2.3004 1.51680 64.20 24 442.7520 21.1551 25 ∞ 3.2000 1.51680 64.20 26 ∞ 1.0297

TABLE 20 Example 7•Specification f 109.87 BF 24.29 FNo. 2.08 2ω [°] 29.4

TABLE 21 Example 7•Moved surface Spacing Infinity 110 cm DD[11] 4.4073 14.30159 DD[14] 19.9236 10.02938

Next, an imaging lens of Example 8 will be described. FIG. 9 is a cross-sectional diagram illustrating a configuration of the imaging lens of Example 8. The imaging lens of Example 8 has the same lens groups and has the same number of lenses as that of Example 1. Table 22 shows lens data of the imaging lens of Example 8, Table 23 shows data about specification, and Table 24 shows data about moved surface spacings. FIG. 17 shows a diagram of aberrations thereof

TABLE 22 Example 8•Lens Data Si Ri Di Ndj νdj  1 103.8430 3.7404 1.95375 32.32  2 265.6927 0.1000  3 86.0594 5.9804 1.59282 68.62  4 −802.5980 0.4828  5 ∞ 1.8504 1.51742 52.43  6 67.2071 4.5996 1.88300 39.22  7 189.9282 1.5273  8 ∞ 1.7714 1.63980 34.49  9 32.7704 10.0753 1.55032 75.50 10 ∞ 8.1423 11 (stop) ∞ DD[11] 12 −304.0663 2.6215 2.10420 17.02 13 −88.3528 1.2286 1.88300 39.22 14 51.3848 DD[14] 15 −270.5800 4.4432 1.55032 75.50 16 −47.6213 1.6334 1.68893 31.16 17 −103.0283 0.1000 18 51.4460 8.7496 1.59282 68.62 19 −76.6667 1.8404 1.76182 26.61 20 76.6667 12.3269 21 121.5127 6.9511 2.00100 29.13 22 −94.5159 20.4244 23 −42.7014 1.5636 1.51680 64.20 24 −236.9069 21.9965 25 ∞ 3.2000 1.51680 64.20 26 ∞ 1.0140

TABLE 23 Example 8•Specification f 112.79 BF 25.12 FNo. 2.12 2ω [°] 28.4

TABLE 24 Example 8•Moved surface Spacing Infinity 110 cm DD[11] 4.9558 13.36234 DD[14] 17.9121 9.505609

Table 25 shows values corresponding to Conditional Expressions (1) to (15) of the imaging lenses of Examples 1 to 8. Further, Table 25 also shows values of the partial dispersion ratios θgF12, θgF31, and θgF33. It should be noted that, in the above-mentioned examples, the d line is set as the reference wavelength, and the values shown in the following Table 25 are values at the reference wavelength.

TABLE 25 Expression Number Conditional Expression Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8  (1) AT/(CT11 + CT12) 0.011 0.011 0.011 0.008 0.011 0.009 0.010 0.010  (2) ν11 32.32 32.32 32.32 32.32 32.32 35.25 32.32 32.32  (3a) ν12 75.50 75.50 75.50 74.70 68.62 81.61 81.61 68.62  (3b) θgF12 − (−0.001682 · 0.023 0.023 0.023 0.021 0.016 0.032 0.032 0.016 ν12 + 0.6438)  (4a) ν/31 75.50 75.50 75.50 74.70 75.50 75.50 67.90 75.50  (4b) θgF31 − (−0.001682 · 0.023 0.023 0.023 0.021 0.023 0.108 0.092 0.023 ν31 + 0.6438)  (5) ν32 31.16 37.01 37.01 31.07 31.16 31.16 31.16 31.16  (6a) ν33 68.62 68.62 68.62 67.73 68.62 68.62 67.90 68.62  (6b) θgF33 − (−0.001682 · 0.016 0.016 0.016 0.014 0.016 0.012 0.014 0.016 ν33 + 0.6438)  (7) ν34 26.610 26.290 26.520 28.460 26.610 26.610 26.610 26.610  (8) f/f2 −1.918 −1.887 −1.882 −1.787 −2.058 −1.815 −1.821 −2.074  (9) f/f1 1.261 1.255 1.255 1.173 1.341 1.205 1.198 1.327 (10) f/f3 1.529 1.516 1.514 1.540 1.546 1.506 1.525 1.571 (11) N2 1.95906 1.84666 1.85896 1.95906 2.1042 1.86631 1.84913 2.1042 (12) ν21 17.47 23.88 22.73 17.47 17.02 21.68 22.54 17.02 (13) N1 1.95375 1.95 1.95375 1.95375 1.95375 1.91082 1.95375 1.95375 (14) Δ ν1r 41.01 37.47 37.47 40.23 41.01 41.01 41.01 41.01 (15) BF/f 0.25 0.25 0.25 0.23 0.21 0.22 0.22 0.22 θgF12 0.540 0.540 0.540 0.539 0.544 0.539 0.539 0.544 θgF31 0.540 0.540 0.540 0.539 0.540 0.625 0.622 0.540 θgF33 0.544 0.544 0.544 0.544 0.544 0.540 0.544 0.544

As can be seen from the above-mentioned data, all the imaging lenses of Examples 1 to 8 satisfy Conditional Expressions (1) to (15), and are imaging lenses in which fluctuations in various aberrations during focusing are suppressed and various aberrations are satisfactorily corrected.

Next, an imaging apparatus according to an embodiment of the present invention will be described. FIGS. 18 and 19 show external views illustrating one configuration example of a mirrorless single-lens camera using the imaging lens of the embodiment of the present invention, as an example of the imaging apparatus of the embodiment of the present invention.

FIG. 18 is an appearance of the camera 30 viewed from the front side, and FIG. 19 is an appearance of the camera 30 viewed from the rear side. The camera 30 comprises a camera body 31, and a release button 32 and a power button 33 are provided on the upper side of the camera body 31. Further, operation sections 34 and 35 and a display section 36 are provided on the rear side of the camera body 31. The display section 36 is for displaying a captured image.

An imaging aperture, through which light from an imaging target is incident, is provided at the center on the front side of the camera body 31. A mount 37 is provided at a position corresponding to the imaging aperture. The interchangeable lens 20 is mounted on the camera body 31 with the mount 37 interposed therebetween. The interchangeable lens 20 is configured such that lens members constituting the imaging lens 1 of the present embodiment are housed in a lens barrel. In the camera body 31, there are provided an imaging element, a signal processing circuit, a storage medium, and the like. The imaging element such as a charge coupled device (CCD) outputs a captured image signal based on a subject image which is formed through the interchangeable lens 20. The signal processing circuit generates an image through processing of the captured image signal which is output from the imaging element. The storage medium stores the generated image. In this camera, by pressing the release button 32, image data, which is obtained through the imaging performed by capturing a still image or a moving image per one frame, is stored in a storage medium (not shown in the drawing) within the camera body 31.

By using the imaging lens according to the present embodiment as the interchangeable lens 20 in such a mirrorless single-lens camera, it is possible to perform focusing at high speed, and it is possible to obtain a high quality video in which various aberrations are satisfactorily corrected.

The present invention has been hitherto described through embodiments and examples, but the present invention is not limited to the above-mentioned embodiments and examples, and may be modified into various forms. For example, values such as the radius of curvature, the surface spacing, the refractive index, and the Abbe number of each lens component are not limited to the values shown in the numerical examples, and different values may be used therefor.

Further, the embodiment of the imaging apparatus has described the example applied to the single-lens digital camera having no reflex finder with reference to the drawings, but the present invention is not limited to this application. For example, the present invention can also be applied to a single-lens reflex camera, a film camera, a video camera, and the like. 

What is claimed is:
 1. An imaging lens comprising, in order from an object side: a first lens group that has a positive refractive power; a second lens group that has a negative refractive power; and a third lens group that has a positive refractive power, wherein during focusing from an object at infinity to a closest object, only the second lens group moves in a direction of an optical axis, wherein a lens closest to the object side in the first lens group and a lens adjacent to the lens closest to the object side on an image side have positive refractive powers, wherein the second lens group includes two or three lenses, wherein the following conditional expressions are satisfied, 0<AT/(CT11+CT12)<0.1  (1), 15<ν11<40  (2), 65<ν12<90  (3a), and 0.0<θgF12−(−0.001682·ν12+0.6438)  (3b), where CT11 is a center thickness of the lens closest to the object side in the first lens group on the optical axis, CT12 is a center thickness of the lens adjacent to the lens closest to the object side on the image side in the first lens group on the optical axis, AT is an air gap on the optical axis between the lens closest to the object side in the first lens group and the lens adjacent to the lens closest to the object side on the image side, ν11 is an Abbe number of the lens closest to the object side in the first lens group, ν12 is an Abbe number of the lens adjacent to the lens closest to the object side on the image side in the first lens group, and θgF12 is a partial dispersion ratio of the lens adjacent to the lens closest to the object side on the image side in the first lens group between a g line and an F line.
 2. The imaging lens according to claim 1, wherein the first lens group has two groups of cemented lenses, where in each group, at least one lens having a positive refractive power and at least one lens having a negative refractive power are combined.
 3. The imaging lens according to claim 1, wherein the third lens group has two groups of cemented lenses, where in each group, at least one lens having a positive refractive power and at least one lens having a negative refractive power are combined.
 4. The imaging lens according to claim 3, wherein one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group includes a lens having a positive refractive power and a lens having a negative refractive power in order from the object side, and wherein the following conditional expressions are satisfied, 60<ν31<90  (4a), 0.0<θgF31−(−0.001682·ν31+0.6438)  (4b), and 15<ν32<45  (5), where ν31 is an Abbe number of the lens which has a positive refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group, θgF31 is a partial dispersion ratio of the lens, which has a positive refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group, between the g line and the F line, and ν32 is an Abbe number of the lens which has a negative refractive power and constitutes one group of the cemented lenses closest to the object side in the two groups of cemented lenses of the third lens group.
 5. The imaging lens according to claim 3, wherein one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group includes a lens having a positive refractive power and a lens having a negative refractive power in order from the object side, and wherein the following conditional expressions are satisfied, 60<ν33<80  (6a), 0.0<θgF33−(−0.001682·ν33+0.6438)  (6b), and 15<ν34<35  (7), where ν33 is an Abbe number of the lens which has a positive refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group, θgF33 is a partial dispersion ratio of the lens, which has a positive refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group, between the g line and the F line, and ν34 is an Abbe number of the lens which has a negative refractive power and constitutes one group of the cemented lenses closest to the image side in the two groups of cemented lenses of the third lens group.
 6. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, −2.5<f/f2<−1.0  (8), where f is a focal length of the whole system in a state where the object at infinity is in focus, and f2 is a focal length of the second lens group.
 7. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 0.9<f/f1<1.5  (9), where f is a focal length of the whole system in a state where the object at infinity is in focus, and f1 is a focal length of the first lens group.
 8. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 1.0<f/f3<2.0  (10), where f is a focal length of the whole system in a state where the object at infinity is in focus, and f3 is a focal length of the third lens group.
 9. The imaging lens according to claim 1, wherein the second lens group includes two lenses, a lens close to the object side in the two lenses has a positive refractive power, a lens close to the image side in the two lenses has a negative refractive power, and the two lenses are cemented.
 10. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 1.70<N2<2.2  (11), where N2 is a refractive index of the lens closest to the object side in the second lens group.
 11. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 15<ν21<30  (12), where ν21 is an Abbe number of the lens closest to the object side in the second lens group.
 12. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 1.65<N1<2.2  (13), where N1 is a refractive index of the lens closest to the object side in the first lens group.
 13. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 30<Δν1r<50  (14), where Δν1r is a difference in Abbe number between a lens closest to the image side in the first lens group and a lens adjacent to the lens closest to the image side on the object side.
 14. The imaging lens according to claim 1, wherein an aperture stop is disposed between the first lens group and the second lens group, and the aperture stop remains stationary during focusing from the object at infinity to the closest object.
 15. The imaging lens according to claim 1, wherein the following conditional expression is satisfied, 0.10<BF/f<0.50  (15), where BF is an air conversion length from an image side surface of the lens, which is closest to the image side, to the image plane, and f is a focal length of the whole system in a state where the object at infinity is in focus.
 16. The imaging lens according to claim 1, wherein the following conditional expression is satisfied. 0.005<AT/(CT11+CT12)<0.05  (1-1)
 17. The imaging lens according to claim 1, wherein the following conditional expression is satisfied. 20<ν11<36  (2-1)
 18. The imaging lens according to claim 1, wherein the following conditional expression is satisfied. 65<ν12<85  (3a-1)
 19. The imaging lens according to claim 1, wherein the following conditional expression is satisfied. 0.01<θgF12−(−0.001682·ν12+0.6438)<0.1  (3b-1)
 20. An imaging apparatus comprising the imaging lens according to claim
 1. 